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Why does the OnDisk size for all Groups and all StorageServers not add up to the same value?

Article ID: 187
Last updated: 18 Oct, 2012

Note: This issue is resolved in V7.0.0

When you add up the OnDisk value for all Backup Groups (or all Backup Accounts) it is often more than the total OnDisk value for all StorageServers. The reason for this lies in de-duplication and is best explained by an example:

Assume you have a brand new Storage Platform with no Backup Accounts or data on it. You create a new Backup Account (Account1) and back up 1 GB of data to it. For simplicity's sake, let's assume the data does not compress. At this point, the OnDisk for Account1 is 1 GB and for the StorageServer it is also 1 GB as expected.

You now create Account2 in the same Backup Group and back up the same data to that Backup Account.  The OnDisk size for Account2 will also be 1 GB, the same as Acount1. Therefore, the Backup Group will now have a total OnDisk size of 2 GB. However, looking at the StorageServer the OnDisk size will still only be 1 GB because of de-duplication.

Therefore the correct mathematical relationships for the OnDisk values are as follows:

sum(Account OnDisk) = sum(Group OnDisk) - this is expected

but due to de-duplication:

sum(Account OnDisk) >= sum(StorageServer OnDisk)

Article ID: 187
Last updated: 18 Oct, 2012
Revision: 5
Views: 2743
Comments: 0
Posted: 06 Sep, 2012 by Marais D.
Updated: 18 Oct, 2012 by Van Rensburg J.
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